” I know nothing about Daniel GCs”.
Why think about retrofitting something when parts are available? The client should buy the correct or recommended parts needed to address any wear and have it serviced. As Bill said, regular maintenance costs need to be budgeted into operating costs. Just like with a car, your costs of ownership continue after purchase too. They need to be aware of this and, if unable to perform the services themselves, find an experienced service provider in their area.

I gathered more information this morning. The price quoted was inline with what I would expect… it just wasn’t inline with what they expected. 

Often, our job is to also help educate the client regarding what is ‘normal’ and what should be planned for.

Sounds like you are referring to “The Danalyzer”. This is a “specialty” product and very different from the typical HP/Agilent GC system. Emerson is a distributor and has probably given them a fair quote for parts. Contact the GC manufacturer (Daniel) for more information (In TX). They provide very good documentation on their products which is easy to obtain. Valves wear out and get contaminated over time. Regular maintenance should always be budgeted into ownership. Optionally, visit the client’s site and look at the systems to determine which valves are used and what parts may be needed.

Yes, it is an online process analyzer. Not a lab analyzer. With 10k members in the group I was hoping there’s some experienced refinery or chemical plant instrument tech or engineer with some helpful knowledge. I didn’t realize Daniel still existed as an entity. I will contact them. Thank you Bill Letter. 

General way to do this is divide and conquer.  What is the error on replicate injections?  Move back one step in your protocol.  WHat is the error there?  Find the places where your error increases the most and focus on them.

Thank you Scott, I have 2-5% error with injection from an autosampler. But I have internal standard, should that not correct for the injection error?

Thank you again!

“Error” and large variation in results have many causes. Please explain how you measured this error? How many replicates did you use? Investigation of any problem requires that we first understand what method you are using. Please provide the detailed GC method used. Please include any sample prep procedures too, as these are just as important as the analysis. Can you tell us if this same method has ever worked for you in the past, and provided much better results (~ 1-2% RSD)? This woudl help put your question into context and allow us to have a discussion about which areas may need to be addressed.

Hi Bill, thank you very much for your reply. My error is relative to my theoretical sample amount, over 2 or 3 repeats. Please see my GC condition in my other comment. I was having this problem for a while and I’m also getting “front inlet pressure shut down” error, could that be a faulty septum?

Thanks again!

It sounds like you may need to address the instrument issues first. Has maintenance been done?

Thank you very much Bill, I will check the maintenance status of the instrument.

Thank you for your reply. My GC conditions are 0.1 uL injection, 250C inlet temperature, 2:1 split ratio, 5 mL/s for flow rate, oven temperature: 50C for 2 min then to 230C at 10C/min. FID detector operates at 400C.

Tao – in addition to my previous comments.
Most split injections work better at >20mls/min in addition 0.1ul injection would cause larger errors. Suggest 0.5ul injection at 10:1 split ratio. This should be equivalent to your current column loading. This should improve your repeatability.
Not sure why you needs FID temperature of 400C?
Hope you do not have a regular vessel graphite ferrule for the jet and it is graphite. 300C should be more than sufficient.

Thank you very much, Gary. I will definitely try that.

Excellent question.  Usually, internal standard will correct for injection error.  The exception to this rule is when you are on the edges of your linearity.  If bias creeps in from high or low signal of IS or analyte, it may not be corrected for.

And the flow rate is … ?

Another abandoned post. They want free help, but make no attempt to answer questions or follow-up.